Northern Ireland Electricity (NEI) said its engineers worked throughout the night to restore the supply to another 1,500 homes and are using a helicopter to check lines in the most hard-to- reach places still affected in the Newry and Downpatrick areas.

Elsewhere, motorists across Ireland have been warned to take extra care on the roads during the cold snap.

All airports across Ireland are open, but passengers flying to and from London's Heathrow have had their flights cancelled.

Met Eireann said wintry showers of rain and sleet will fall in Leinster and Ulster throughout the day, with some dry or bright spells in Munster and Connacht.

A widespread sharp or severe frost is expected overnight, with temperatures as low as minus 4C, resulting in icy stretches on roads and patches of freezing fog.